For environmental reasons government authorities are increasingly either encouraging or requiring household occupants to recycle their waste products. In the past this was typically limited to dry waste such as leaves and lawn clippings, glass, paper and tin but, more recently, compostable wet waste materials such as food and table scraps are also being considered recyclable (through the use of cellulose-lined paper compostable bags).
According to some of the known and used manufacturing methods for wet waste bags an inner polymer layer is laminated to an outer paper layer(s) using heat to activate glues such as starches and/or to melt and seal the film coatings. However, such methods are disadvantageously expensive because they require much heat energy, involve multiple-step processing (in order to provide heating and drying periods for the glues) and require the purchase of relatively expensive hot application glues. Moreover, even if such polymer layers are comprised of biodegradable materials they typically do not degrade into compost as efficiently as does a cellulose film and, more disadvantageously, they are not permeable to allow the transfer of water vapour and oxygen there through which means that any bags lined with these materials cannot satisfactorily store wet waste such as food waste over any significant period of time because such wastes will undergo an anaerobic decomposition when the bag is sealed and exude foul odours.
Cellulose films provide substantial advantage over polymer films in that they are permeable to water vapour and oxygen yet are generally impermeable to liquid (note that although there exist cellulose films which are also permeable to liquid these types of films are not contemplated herein and all references herein to cellulose film refer to those films which are generally impermeable to liquid). However, they have associated with them two disadvantages, one being that they are relatively brittle and tend to break when stressed and the other being that they are degraded and damaged by heat. Consequently, a lamination of cellulose film to paper using the usual heat processes to heat the plasticized surfaces of the cellulose and affix it to the paper would cause damage to the cellulose and the resulting bag product would have a limited shelf life and low handling tolerance (since the cellulose layer would be prone to an early breaking and tearing away from the paper layer). Since the purpose of the bag is to effectively contain wet waste over a period of time, and the cellulose layer is used to retard the transfer of liquid (moisture) from the inside to the outside of the bag, such damage to the cellulose layer renders the product ineffective and unsuited to its purpose.
To minimize such heat exposure, reduce adhesive material usage and avoid blockage of the permeable membrane provided by the cellulose, it is known to apply glues to the cellulose in patches or strips. For example, U.S. Pat. No. 5,178,469 which issued to Woods End Research Laboratory on 12 Jan. 1993 discloses a biodegradable bag having a cellulose lining which is affixed to the paper layer using an adhesive which is applied, using drip feeders, in spaced strips between the paper and cellulose layers. However, such an uneven coverage of adhesive between the paper/cellulose layers produces relatively large spacings between the points of attachment of the cellulose and produces stress points at each new strip (patch boundary). In such products, where the cellulose joins to the paper there is an increased tendency of the cellulose to tear at these stress points. Also, such drip feeder means of applying glue is inherently inaccurate and disadvantageously wastes a significant amount of glue material.
A further disadvantage with the prior methods and means of making compostable bags is the excessive and/or ineffective usage of adhesives in the formation of the bag bottom. According to known processes the bag bottom is formed using adhesive applied by fixed roller applicators with a drip feed and this does not allow any control over the application either with respect to location or deposition volume. Since it is important that the bag bottom be fully closed off (i.e. sealed) to avoid leakage of liquid it is important that the score lines of the bag bottom and other fold areas of the bag bottom be effectively glued. Also, since biodegradable adhesives are relatively costly it is important that wastage of the glue be avoided and imprecise glue application means are inherently wasteful and non-economic.
Therefore, it is desirable to provide a cost effective means of making a wet waste compostable bag which allows for use of a cellulose layer without the application of heat thereto yet securely and fully adheres the cellulose to the paper layer without producing substantial stress points and with minimal interference of the permeability of the cellulose to water vapour and oxygen. Further, it is desirable to provide a means of more precisely and efficiently applying adhesive to those areas of the bag, particularly the bag bottom, which require placement of adhesive at specific locations for an effective formation of a wet waste bag.